In manually operated cooking appliances, such as a cooktop, for example, a burner is turned on or activated by means of manually operating an associated knob. To turn on a burner, a user turns the corresponding knob from an OFF position, and the power of the burner is regulated depending on the degree of opening of the knob (depending on the angular position of the knob with respect to the OFF position).
Knobs are known to comprise an associated illumination to inform the user that the burner is on, and in some cases to furthermore indicate the power of the burner. Illumination has been provided up until now in two different ways that are described below in a simplified manner. In both cases, the illumination system comprises, associated with the knob, an illuminating device and an activation switch which is closed when the knob is turned from the OFF position.
On one hand, as schematically shown in FIGS. 1a and 1b, there are illumination systems in which there are provided two independent electric circuits C1′ and C2′ for each knob 201′, one for the activation switch 1′ and another for the illuminating element 2′ (which can be, for example, a LED). This solution is flexible as it allows providing information to the user even when the corresponding burner is inactive (when the activation switch 1′ is open), however, it has the drawback of requiring a large number of cables per knob 201′ from a corresponding electronic module 4′ (in charge at least of feeding the electric circuits C1′ and C2′), particularly four: two cables 11′ and 12′ for the first electric circuit C1′ and two cables 21′ and 22′ for the second electric circuit C2′. This makes it an expensive and difficult-to-implement solution which will become more expensive and complex the more burners the cooking appliance in question comprises (FIG. 1b schematically shows the connection of two knobs 201′, corresponding to a cooking appliance with two burners).
On the other hand, in order to solve or prevent this complexity and reduce cost, illumination systems in other solutions comprise a single electric circuit C″ for each knob, as schematically shown in FIG. 2. This solution is simple and does not require too much wiring, but it has the drawback of not being able to provide any type of information when the activation switch 1″ is open, given that the display device 2″ cannot be lit up in those circumstances.
An illumination system with a single electric circuit is disclosed in patent document U.S. Pat. No. 6,733,146 B1. In this illumination system, the activation switch is connected between the power supply and the corresponding display device. The activation switch allows connecting the display device to the power supply only when the knob is not in the OFF position. In this embodiment, the power supply is a battery arranged in the knob itself, so cables are dispensed with.